The invention relates to well packer devices of the type customarily used in the production of petroleum effluents from wells. The packer seals the annulus between the well casing and the production tubing string through which the well effluents flow to the surface. These packers are sometimes employed to provide seals for injecting fluids into the well and for a variety of other purposes.
The prior art packer design usually includes an annular resilient seal, a mechanical anchor or slips and a downwardly facing spreading cone. The packer is set by lowering the cone behind the slips which extends the slips into tight frictional engagement with the surrounding casing to anchor the packer in place. During this setting action, the packer seal is also compressed so that it expands radially into sealing engagement with the tubing and casing to seal the annulus. In conventional weight-set packers, the packer seal and slips are held in set, extended position by the tubing weight.
In many instances, as for example when weighted well fluids are to be displaced from the well to permit the well to flow, it is desirable to simultaneously flow fluids through both the tubing and the annulus after the packer has been placed at the desired subsurface location. One prior art weight set packer design provides a bypass through the packer for this purpose. The bypass is opened, after the packer is set, by raising the tubing string sufficiently to remove a tubing seal from its seat. With the bypass opened, the weighted fluids are displaced from the well by pumping lighter fluids down through the tubing. The lighter fluids exits the bottom of the tubing and, together with the displaced weighted fluid, flows to the well surface through the annulus and bypass.
The upward flow of the well fluids through the bypass of the described prior art packer exerts a lifting force on the set packer. Since the tubing weight is removed from the packer while the bypass is opened, the pressure induced force may be sufficient to cause the packer to release and move upwardly through the casing. The orientation of the single spreader cone is such that it wedges the slips to prevent only downward movement of the packer and is thus ineffective in preventing such upward packer movement.
When the top of the tubing is lowered into place in the well head, if the packer position has been raised, excessive tubing weight may be rested on the packer which in turn may damage both the packer and the tubing. This danger is controlled in part by maintaining a relatively slow pumping rate so that the packer remains at the proper location.
Under normal producing conditions, the pressure in the well annulus is greater below than above the packer seal. The resulting pressure differential creates upwardly directed forces which, in some instances, may unset the packer even with the proper tubing weight resting on the packer. To avoid this problem, the prior art packer previously described employs "hydraulic hold-down buttons" in the packer body. The pressure differential creates forces which extend the buttons into frictional engagement with the well casing to assist in holding the packer in place. Whie these hold-down buttons are effective in preventing pressure induced release of the set packer, they are objectionable to the extent that they require the use of resilient, slidable seal rings which are prone to leakage.
An alternative design for preventing pressure induced packer release requires the use of upper and lower opposed cone members which are moved toward each other to extend slips disposed between the cones. Movement of the set packer in either direction is prevented by the action of the two cones which increase the slip's gripping force in response to an increase in the forces tending to move the packer in either direction.
While dispensing with the need for hydraulic hold down buttons and their attendant leakage danger, the dual cone design when employed in mechanically set packers has conventionally required that the tubing string be rotated in order to release the packer from set position. Longitudinal movement of the tubing relative to the set packer is also not usually possible with such a design so that such movement cannot be employed to open a bypass through the packer. Rotation of the tubing for any reason may be undesirable in extremely deep or deviated well bores or where the well is being completed from a floating drilling rig. Certain hydraulically set packers employing dual cones can be released by non-rotative manipulation of the tubing string, however, hydraulically set packers are generally more expensive and have a longer length than mechanically set packers. Short packers are desirable in deep and highly deviated wells since they are easier to handle and reduce the danger of sticking.
The same pressure induced forces which tend to unseat the packer may also tend to open the bypass by pushing the tubing seal out of the set packer. The described prior art packer prevents such pressure induced movement of the tubing with a spring loaded sleeve having two sliding seals. The effective area across the sliding seals produces a net downwardly directed pressure induced force is produced on the sleeve. A collet assembly carried on the sleeve compresses the spring and transmits the induced force to the tubing so that the pressure induced forces tending to drive the tubing upwardly through the packer are always less than those tending to drive the tubing downwardly. The spring retains the sleeve and its attached collet in cocked position, ready to engage and lock the tubing, when the bypass is opened and no pressure differential exists across the sleeve's sliding seals.